Integrated circuit assemblies are employed in a wide variety of electronic applications. Increasing demand for high performance yet reliable electronic products that are ever smaller, lighter, and cost effective has lead to corresponding demands on the manufacturers of integrated circuit assemblies.
Such circuit assemblies have traditionally employed a circuit board and at least one electrical component (e.g., an integrated circuit device) connected to the circuit board by a plurality of connectors, wires and/or solder bumps. It has been known that differences between the coefficients of thermal expansion (CTE) of the circuit board and electric component can contribute to early fatigue failure of solder interconnections, especially during thermal cycling of the circuit assembly. Differences in CTE are especially problematic for integrated circuit assemblies used in environments subjected to high temperatures, such as applications in close proximity to internal combustion engines, i.e., on-board motor vehicle applications.
Epoxy resins have been used in the manufacture or integrated circuit assemblies. In some cases, such resins are disposed between the electric component and circuit board to anchor or adhere the electronic component to the circuit board, to encapsulate and protect the connectors, and/or to mitigate the differences between the CTE's of the components of the circuit assembly.
For example, epoxy resins have been utilized as underfill materials in the manufacture of integrated circuit assemblies having a flip chip construction. Underfill materials are intended to support and protect the electrical connections of the flip chip while simultaneously reducing the thermal-mechanical stress on the flip chip connections.
Known epoxy resins have generally been unable to provide cured underfill materials having a desirably low CTE. Epoxy resins having a CTE of less than 60 ppm/° C. are especially advantageous in mitigating the differences between the CTEs of the die and circuit board. Suitable epoxy resin compositions have often been achieved only with the use of significant amounts of CTE-reducing fillers.
Unfortunately, the use of such fillers has traditionally resulted in increased manufacturing challenges and problems.
For example, circuit assembly manufacturing processes using capillary-flow underfill technology typically require introduction of an epoxy resin based underfill composition into the interstitial spaces of an integrated circuit assembly. The presence of CTE-reducing fillers in such compositions can result in an increased viscosity that impedes the flow and distribution of the underfill composition, and/or causes damage to delicate electronic components. Such processes are often characterized as unacceptably long and/or costly.
In no-flow underfill processes, the epoxy based underfill material is typically applied to the surface of an integrated circuit substrate, To join a flip chip to the substrate, the bumps of the flip chip are pushed through the underfill material until the flip-chip bumps make contact with corresponding substrate bond pads. In this case, filler particles can become undesirably trapped between the flip-chip bumps and the corresponding substrate bond pads.
Thus, epoxy resin based compositions having low amounts of CTE-reducing fillers are advantageous as compared to those having greater amounts of CTE-reducing filler.
In addition, epoxy resins useful in the construction of integrated circuit assemblies must also have a reaction profile that accommodates the reflow profile of the solder used therein. In particular, it would be highly desirable if the solder reflowed before substantial cross-linking of the epoxy resin occurs. However, cross-linking must progress quickly once solder reflow has occurred.
Thus, known epoxy resins have not fully resolved challenges associated with the design and manufacture of integrated circuit asseremblies, especially flip chips.